The present invention generally relates to apparatus for polishing or planarizing workpieces, such as silicon wafers, and, more particularly, to a seal used in conjunction with such apparatus.
In the semiconductor manufacturing industry, silicon workpieces are used as substrates for the fabrication of integrated circuit components. The workpieces, known in the industry as xe2x80x9cwafersxe2x80x9d, typically are sliced from an elongated cylinder, or bole, of single crystal silicon, and they generally have a flat, circular, disk-like shape. During the fabrication process, the wafers usually undergo multiple masking, etching, and dielectric and conductor deposition processes to create microelectronic structures and integrated circuitry on the wafers. Since the character of the substrate surface may substantially impact the quality of the integrated circuitry formed upon that surface, careful preparation of the wafer surface is usually necessary throughout the various stages of the semiconductor fabrication process. Moreover, as rapid evolution in the industry provides a continual impetus for diminishing the size of integrated circuits while heightening the density of the microelectronic structures forming each circuit, the need for precise preparation of wafer surfaces becomes evermore critical in the fabrication of high-quality semiconductors.
The extremely precise surface configuration of the substrates used in the production of integrated circuit components generally can be obtained by appropriately planarizing or polishing the substrate surface. Chemical mechanical planarization or polishing (CMP) machines have been developed for this purpose and are used to ensure that the substrate is free from projections or other imperfections which might adversely affect the accuracy and performance of the microelectronic structures formed thereupon. Such CMP machines and processes are well known in the art and are commercially available. For a discussion of CMP processes and apparatus, see, for example, Arai, et al., U.S. Pat. No. 4,805,348, issued February, 1989; Arai, et al., U.S. Pat. No. 5,099,614, issued March, 1992; Karlsrud et al., U.S. Pat. No. 5,329,732, issued July, 1994; Karlsrud, U.S. Pat. No. 5,498,196, issued March, 1996; and Karlsrud et al., U.S. Pat. No. 5,498,199, issued March, 1996.
Conventionally, a CMP polishing apparatus includes a rotatable platen and a wafer carrier which each rotate about their respective vertical axes at individually selected speeds. As seen in FIGS. 1 and 2, a conventional abrasive polishing pad 126 is attached to the upper surface of a rotatable platen 128 which rotates by means of a rotary shaft (not shown). An upper portion of the rotary shaft is connected to the rotatable platen 128 and a lower portion of the rotary shaft is connected to a motor (not shown) which rotates the shaft as needed. A semiconductor wafer seated in the wafer carrier 124 is lowered into engagement with the polishing pad 126 and clamped between the carrier 124 and the rotatable platen 128, typically through the exertion of downward force by the carrier 124. The polishing pad 126 polishes the wafer surface by rotating when the wafer is brought into engagement with the polishing pad 126 by wafer carrier 124. A liquid containing an abrasive, granular material, known as a slurry, is deposited onto and retained by the polishing pad 126. During operation of the CMP apparatus, the wafer carrier 124 exerts pressure on the rotatable platen 128, and the surface of the semiconductor wafer held against the polishing pad 126 is thereby planarized and/or polished by a combination of chemical planarization and/or polishing by the slurry and mechanical planarization and/or polishing by the pad 126 as the carrier 124 and the rotatable platen 128 are rotated, respectively.
The rotatable platen that supports the polishing pad typically is mounted to, supported upon, and rotated by a rotary shaft that is coupled to a motor. A conventional rotary shaft assembly is illustrated in FIG. 3. The rotary shaft assembly 300 includes a rotary shaft 302 which passes through a hollow, non-rotatable housing 304 having a plurality of interior components, such as internal bearings 306 which support the shaft 302 and permit relative rotation between the shaft 302 and the housing 304; spacers 308; and seals (not shown). In order for the rotary shaft 302 to rotate about its vertical axis while supporting the platen 128 above the non-rotatable housing 304, a void space or pocket 310 exists between a portion 301 of the rotary shaft 302 and an upper portion 305 of the assembly housing 304. Typically, the void space 310 comprises a conventional step-tooth labyrinth seal 312 formed between portion 301 of the rotary shaft 302 and upper portion 305 of the assembly housing 304. The particular configuration of labyrinth seal 312 is intended to prevent fluid, such as slurry, introduced onto the polishing pad 126 during the polishing process, from entering the assembly housing 304.
During the polishing process, slurry frequently flows off the polishing pad 126 in the direction of arrow 314 and collects or pools at the opening of the labyrinth seal 312. As the process continues, the heat generated by the rotation of the shaft 302 results in an increase in the temperature within the assembly housing 304. This increased temperature frequently results in an eventual build-up of negative pressure within the assembly housing 304 as the components within the assembly housing 304 cool, which build-up of negative pressure effects a suction force on the slurry which has collected at the opening of the labyrinth seal 312. Consequently, the slurry is drawn through the labyrinth seal 312 and into the housing 304 of the rotary shaft assembly 300, where the slurry then gets trapped between the rotary shaft 302 and the internal bearings 306, seals (not shown), and/or other stationary components of the assembly 300. Any slurry which is interposed between or among the interior components of the rotary shaft assembly 300, such as the bearings 306 for example, has a potentially corrosive and/or degenerative effect on the components which tends to cause premature and excessive wear as well as damage that compromises the functioning of the apparatus.
Presently known rotary shaft labyrinth seals are unsatisfactory in several regards. Specifically, prior art devices have proved to be ineffective at preventing abrasive or corrosive chemical slurry, slurry vapor, and other fluids from entering the shaft assembly and deteriorating or destroying the interior components of the assembly. For example, during the polishing process, the step-tooth design of current labyrinth seals permits slurry to collect in the valley created by the labyrinth opening. As the temperature naturally rises and falls within the housing of the rotary shaft assembly over the course of the polishing process, a negative pressure within the assembly housing is created, and the slurry which has collected in the opening of the labyrinth is drawn through the labyrinth and into the assembly housing. The slurry then gets trapped between the rotary shaft and the internal bearings, seals, and/or other stationary internal components of the assembly. Since typical CMP shaft assemblies do not permit post-manufacture application of additional grease to the internal bearings in the shaft assembly, deterioration and corrosion caused by slurry and/or slurry vapor entering the assembly effectively shortens the useful life of the bearings and therefore of the rotary shaft assembly. Moreover, the gradual deterioration and particle degeneration of various assembly components ultimately may contaminate the polishing process and compromise the overall quality of the wafer fabrication process. Consequently, deficiencies in prior art labyrinth seals likely contribute significantly to premature wear and damage of assembly components, incrementally inferior machine performance, and, eventually, destruction of the rotary shaft assembly, all of which generally result in increased machine down-time and maintenance costs, decreased wafer through-put, and, ultimately, increased wafer fabrication costs.
In view of the foregoing, a need exists for a seal which overcomes the shortcomings of the prior art. Thus, there is a need for a seal which inhibits slurry, slurry vapor, and other fluids associated with substrate finishing processes from entering the rotary shaft assembly. There is also a need for a seal which inhibits fluids, slurry, and slurry vapor from collecting at the opening of the labyrinth and then being drawn through the labyrinth and into the shaft assembly as the temperature of the shaft assembly rises and falls during the polishing process. Additionally, there is a need for a seal which inhibits corrosion and deterioration of the interior components of the shaft assembly by fluids and/or slurry used during the polishing process.
The present invention provides a seal having improved reliability characteristics, which are useful in apparatus employed in the preparation of substrate surfaces, such as the surfaces of semiconductor wafers. Preliminarily, as used herein, the seal is generally referred to as a xe2x80x9clabyrinth sealxe2x80x9d, though one skilled in the art will appreciate that other types of seals may likewise be substituted and still fall within the ambit of the appended claims. Thus, in accordance with one aspect of the present invention, there is provided a rotary shaft labyrinth seal comprising a member having at least one sloped feature which is configured to substantially inhibit a fluid or other material used in substrate processing from entering into the labyrinth seal and contacting the interior components of the rotary shaft assembly during or after a substrate preparation process. In an exemplary embodiment, the labyrinth seal comprises a sloped surface having a base and an apex, wherein the base juxtaposes the opening of the labyrinth seal. In another exemplary embodiment, the labyrinth seal comprises a sloped surface having an apex and a base, wherein the base juxtaposes the opening of the labyrinth seal; and a surface, wherein the surface extends outwardly from the base and toward the opening or entry of the labyrinth seal.
In accordance with another aspect of the invention, a labyrinth seal is used in conjunction with a wafer polishing apparatus, such as a chemical planarization apparatus. In one exemplary embodiment, there is provided a workpiece polishing apparatus including a rotary shaft assembly which comprises a housing having a plurality of interior components; a shaft extending longitudinally through the housing, wherein the shaft includes a first end connected to a motor for rotating the shaft about its vertical axis; a platen connected to a second end of the shaft; and a labyrinth seal located in a space between the second end of the shaft and the housing, wherein the labyrinth seal comprises a member having at least one sloped feature which is configured to inhibit a fluid or other material used in substrate processing from entering into the labyrinth seal and contacting interior components of the rotary shaft assembly during or after a substrate preparation process.
Other features and advantages of the present invention will become apparent to those skilled in the art from the following detailed description. It should be understood, however, that the detailed description and specific examples, while indicating exemplary embodiments of the present invention, are given for purposes of illustration only and not of limitation. Many changes and modifications within the scope of the instant invention may be made without departing from the spirit thereof, and the invention includes all such modifications.